VT-269

This exhibit was last updated on 21 February 2014

The VT-269 is a most interesting valve. It was made in America on 31st January 1944 and packaged in a buff cardboard box. It was made for military service with the US Army and Navy.

The valve is a type 717A is known as a 'little doorknob'. VT-269 is a US Government designation for Vacuum Tube 269.

Intended as a low-noise front-end amplifier in UHF radar receivers, the 717A achieves 4 mA/V despite its small size. Designed by Western Electric, the 717A was made in large numbers by several US manufacturers during WWII. It was a successful valve although it was soon superseded by improved (and cheaper) all-glass types.

The inset photograph shows the construction, this sample arrived with a broken envelope, and thus afforded a close view of the electrode assembly. For scale the width between the flats in the base circle is 9 mm. The picture shows indirectly heated cathode, three wire wound grids on notched rods and a cylindrical anode. This pentode lays flat across the pressed glass base of the envelope and the electrode structure is small enough to fit into the B7G miniature envelope that was introduced into the UK after WWII. This design is a hybrid between traditional construction and the all glass valves. Similar experimentation with glass base construction is shown by the metal valves from 1935 and also the earlier acorn valves.

An interesting point is why make this valve on an IO base when the technology of all glass production existed in America in the mid 1940s. I suspect that for volume production the equipment and trained staff were more readily available across the whole manufacturing industry for Octal base production.

See alsoacorn valves and why they were blacklisted during WWII by the UK Government.